This application is based on Japanese Patent Application No. 11-30648 (1999) filed Feb. 8, 1999, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a curing characteristics measuring apparatus which is capable of measuring curing behaviors of a thermosetting resin or a composite material containing the same and to a curing characteristics measuring method.
2. Description of the Related Art
To know whether or not a thermosetting resin or a composite material containing the same has predetermined characteristics after curing, or, whether or not curing thereof begins and completes in a predetermined time under a specific temperature or pressure, a curing characteristics test is performed. For this purpose, a test has heretofore been conducted by partly changing the shape of a die of a viscoelasticity tester for measuring vulcanization characteristics of rubber (hereinafter referred to as xe2x80x9cvulcanization testerxe2x80x9d).
Vulcanization testers for rubber are described in ISO3417, ISO6502, JIS K6300 and the like. Further, testers having a die devised for curing characteristics test of themosetting resins are described in Japanese Patent Application Publication No. 7-72710 (1995), Japanese Utility Model Application Publication No. 5-2841 (1993) and the like. The above-described vulcanization tester is an apparatus in which an unvulcanized rubber sample is charged in a sample chamber having a fixed surface and a rotation-vibrating drive surface, a torsional vibration is applied to the sample through the drive surface to record the changes as a curve while measuring a shearing stress generated in the sample as a vibration torque through the fixed surface or the drive surface. Still further, the die devised for curing characteristics test of thermosetting resins has devised grooves provided on the surface to prevent slipping between the die surface and the sample.
A thermosetting resin or a composite material containing the same is large in degree of volume contraction associated with curing reaction as compared to vulcanization reaction rate of rubber. Hereinafter this phenomenon is referred to as xe2x80x9ccuring shrinkagexe2x80x9d. In the prior art curing characteristics test apparatus, even if provided with the above-described slipping prevention grooves, when the curing shrinkage is considerable, in the curing process of the sample, a gap is generated between the inner wall of the sample chamber and the sample, resulting in such problems that a torsional vibration provided from the drive surface is not effectively transmitted to the sample, and/or a shearing stress generated in the sample is substantially damped before it is transmitted completely to a torque detection mechanism. Therefore, with such a test apparatus, there is no reproducibility of data and only part of necessary characteristics can be measured.
Group (A) of curves in FIG. 1 shows a practical example of such unsatisfactory test results. These are examples measured by repeated measurements by a prior art test apparatus of a sample which causes volume contraction during curing reaction. The test apparatus used is equipped with a die devised for curing characteristics test of thermosetting resin, which is described, for example, in Japanese Patent Application Publication No. 7-72710 (1995), Japanese Utility Model Application Publication No. 5-2841 (1993).
A prior art apparatus and measuring method will be described using a practical example. Construction of a measuring apparatus which presently is widely used is exemplified in FIG. 2. By rotation-vibration of a drive shaft 8, a torsional vibration is applied to a sample charged in a sample chamber 26 through a drive die 2 directly linked to the shaft 8, and a shearing stress generated inside the sample is transmitted in the form of a vibration torque to a torque detection die 1. Since the torque detection die 1 is supported by a torque detection mechanism 14 through a torque detection shaft 7, the vibration torque and a temporal change thereof are recorded by electrical means or the like through the torque detection mechanism 14.
The sample chamber 26, in addition to the torque detection die 1 and a drive die 2, comprises a torque detection side fixed die 3, and a drive side fixed die 4. Of these, the upper part from the torque detection die 1 and the torque detection side fixed die 3 is movable in upward and downward direction in the figure by an air cylinder 23 when loading/unloading the sample. On the other hand, since the drive die 2 and the drive side fixed die 4 are fixed with respect to the vertical direction in FIG. 2, the sample charged in the sample chamber 26 is maintained in a sealed state during measurement by a tightening pressure of the air cylinder 23. All the components constituting the sample chamber 26 are maintained at a predetermined measurement temperature by means of appropriate heater/temperature controllers 19, 20, 21 and 22. Numeral 5 indicates an upper seal, 6 is a lower seal, 10 is a motor, 11 is an eccentric rotary shaft, 12 is a crank arm, 13 is a torque arm, 15 and 16 are heaters, 17 is an upper base supporting an upper measuring part B and the like comprising the upper die 1 and the upper fixed die 3 and the like, 18 is a lower base supporting a lower measuring part A and the like comprising the lower die 2 and the lower fixed die 4 and the like, and 24 is a flash collector. Detailed construction in the vicinity of the sample chamber 26 is shown in FIGS. 3 and 4. Description of the respective figures will be made along with description of the measurement examples described below.
In FIG. 3, numeral 66 indicates a sample, 66A is a sample overflowed into the flash collector. In FIG. 4, numeral 64A indicates a cutout part of a seal plate support plate 64, 65A is a collar part of a seal plate 65, and 69 is a spot facing hole for a fixing screw.
The sample 66 used in the measurement example in FIG. 1 is an unsaturated polyester type thermosetting resin. This sample 66 is a viscous liquid having a fluidity at room temperature, and its volume contraction associated with curing is as large as about 7%. This value is one of the largest values among themosetting resins. The sample 66 is injected into the sample chamber 26 in FIG. 2. FIG. 3 shows an enlarged diagram of the sample chamber 26. The shape of a torque detection die (upper die) 61 shown in FIG. 3 is conical form, different from the example in FIG. 2, however, there is no substantial difference even if it is in a disk form. In addition, in the description hereinafter, for simplicity, the torque detection die 61 is referred to as an upper die, a torque detection side fixed die 63 as an upper fixed die, a drive die 62 as a lower die, and the seal plate support plate 64 as a lower fixed die.
FIG. 4 shows an exploded perspective diagram of components constituting the sample chamber 26. The seal plate 65 and the seal plate support plate 64 combinedly function as the lower fixed die, however, for convenience of removing cured sample and cleaning after the completion of measurement, the seal plate support plate 64 and the seal plate 65 have a separable structure.
After injecting the sample 66, the sample chamber 26 is rapidly closed, and driving of the lower die 62 shown in FIG. 3 is started. The driving is performed in sinusoidal rotation-vibration of an amplitude angle of xc2x1xc2xc degree at a frequency of 1.6 Hz about the drive shaft 8 shown in FIG. 3. This rotation-vibration is transmitted to the sample 66 to generate a shearing stress according to its viscoelasticity inside the sample, which is transmitted as a vibration torque to the torque detection shaft 7 through the upper die 61 shown in FIG. 3. The vibration torque is detected by the torque detection mechanism, which is directly connected, and the state of temporal changes thereof is recorded as a curve. Normally, in this curve, only amplitudes of torque sinusoidal wave are recorded.
Temperatures of the five parts constituting the above sample chamber, namely, the upper die 61 shown in FIG. 3, the lower die 62, the upper fixed die 63, the seal plate 65, and the seal plate support plate 64 are controlled by the heaters 16, 20, 21, and 22 shown in FIG. 2 and temperature controllers (not shown), and maintained at a predetermined temperature (130xc2x0 C. in the present example). As a result, temperature of the sample 66 maintained at room temperature begins to increase at the same time it is injected into the sample chamber, and rapidly reaches a predetermined curing temperature.
At the same time the air cylinder 23 is moved down to close the sample chamber 26, driving of the lower die 62 is started, and the vibration torque is detected. A record of temporal changes of the detected torque amplitude is the group (A) of curves shown in FIG. 1, which is referred to as a curing behavior curve or a curing curve. The group (A) of curves shows repeatedly measured results of the same sample under the same conditions. Group (B) of curves will be described later. The axis of abscissas of FIG. 1 indicates the passage of time (min) from sample charge, and the axis of ordinates indicates amplitude values of vibration torque corresponding to each time passage. The injected sample 66 from an initial flexible and fluid state rapidly begins to cure after a certain time lapse, and while decreasing curing rate with the progress of curing, reaches a hard saturation state in due course of time. The state of this series of thermal curing process can be seen from the group (A) of curves in FIG. 1. The time at which rapid curing begins is referred to as a curing start time, and a curing reaction rate can be determined from gradient of the curve after curing start and changes thereof. The two factors of the curing start time and the curing reaction rate are respectively important industrial indices characterizing the rate of reaction at that temperature of the resin sample, which is largely varied with the curing temperature. Further, a torque of the part in which the curing curve of the latter half is almost flat (hereinafter referred to as an after-cure torque) is a measure of hardness of the cured resin at that temperature, which is normally soft as the measuring temperature increases, that is, it has a heat softening type temperature dependence. Therefore, to know these three factors and the relationship between these factors and temperature quantitatively means to obtain an important guideline for quality control and process design of the resin composition, and in performing material design of compositional formulation and construction of the composite material itself.
In practice, however, as shown in the curve group (A) of FIG. 1, it is often that the curing curve in the latter half of curing process is disturbed and repeatability is not obtained. This is a phenomenon which is conspicuous when curing shrinkage is large. A cause therefor is considered as due to the fact that pressing force important for slip prevention in the interface between the sample and the upper and lower dies is decreased with the progress of the reaction, depending on the magnitude of shrinkage, resulting in a gap on the interface, the vibration torque is largely damped during the time when it is transmitted in the course of the drive diexe2x86x92 samplexe2x86x92 torque detection die. In such a case, among the above three factors, although some quantitativity is obtained as to the curing start time, quite no quantitativity is obtained for the remnant two factors.
As described above, when curing behaviors of thermosetting resins are measured by the prior art curing characteristics measuring apparatus, there have frequently occurred problems in that a gap is generated between the sample and the sample chamber in association with curing shrinkage characteristic of thermosetting resins, therefore, torsional vibration provided from the drive surface is not effectively transmitted, and/or shearing stress generated in the sample is substantially and randomly damped before it is completely transmitted to the torque detection mechanism, resulting in incapability of exact measurement.
It is therefore an object of the present invention to provide a curing characteristics measuring apparatus and measuring method which solves such prior art problems and is capable of exactly and efficiently measuring the curing curve.
In accordance with the present invention which attains the above object, there is provided a curing characteristics measuring apparatus characterized in that a separable sample chamber having a fixed surface and a rotation-vibrating drive surface is charged with a sample having a viscoelasticity, a torsional vibration is applied to the sample through the drive surface, and a shearing stress generated in the sample is measured as a torque through the fixed surface or part thereof, wherein means is provided for changing volume of the sample chamber following volume change generated in curing process of the sample.
The means for changing volume of the sample chamber comprises a structure wherein at least one of the drive surface and the fixed surface is movable in a direction of changing an interfacial distance between both surfaces, a means for achieving the movement following volume change generated in curing process of the sample.
The drive surface is a sample contact surface of a drive die, the fixed surface is a sample contact surface of a torque detection die, a torque detection side fixed die and a seal plate, and the movable structure is provided with a spring function capable of deflecting in a direction of changing an interfacial distance between the drive surface and the fixed surface.
The means for achieving the movement uses air pressure as a drive source. A value of the air pressure is possible to be varied according to a change in shearing stress in curing process of the sample.
A curing characteristics measuring method of the present invention characterized in that a separable sample chamber having a fixed surface and a rotation-vibrating drive surface is charged with a sample having a viscoelasticity, a torsional vibration is applied to the sample through the drive surface, and a shearing stress generated in the sample is measured as a torque through the fixed surface or part thereof, wherein a measurement is performed while changing volume of the sample chamber following volume change generated in curing process of the sample.
The measurement is performed while changing volume of the sample chamber by moving at least one of the drive surface and the fixed surface in a direction to change interfacial distance between both surfaces.
The sample is contacted with a rotation-drive surface of a drive die, surfaces contacting with the sample of the torque detection die, the torque detection side fixed die and the seal plate are fixed with respect to rotational direction of drive die, and a support body for supporting the seal plate is provided with a spring function capable of deflecting in a direction of changing an interfacial distance between the drive surface and the fixed surface, thereby reducing volume of the sample chamber in accordance with a volume contraction generated in curing process of the sample.
The movement is achieved using air pressure as a drive source.
A value of the air pressure is varied according to a change in shearing stress in curing process of the sample.
As described above, with the present invention, following the phenomenon that the thermosetting resin sample shrinks in the curing process, volume of the sample chamber comprising the drive surface of the drive die and the torque detection surface of the fixed die is reduced, and appropriate contact bonding conditions are always maintained between the sample and the drive surface and between the sample and the torque detection surface, thereby preventing slip on the interface thereof and efficiently detecting and recording exact curing curves over the entire curing process of the sample.
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.